Extra Message in flat file -- Input truncated to 9 characters

when I use the following script to generate a flat file, I am getting
the Input truncated to 9 characters message in the flat file.
Please let me know how to avoid this message.

The script used to generated the flat file is,

set head off
set pages 0
set feed off
set serveroutput on size 1000000
set line 10
whenever sqlerror exit 9
spool d:\a.txt
SELECT RPAD('AA',10,'0') FROM DUAL;
set line 8
SELECT RPAD('B',8,'0') FROM DUAL;
set line 15
SELECT RPAD('C',15,'0') FROM DUAL;
spool off